Patent GB-685620-A (GB)
Title: Improvements in and relating to the concentration or dehydration of di-propylamines
IPC: B01D3/14
Filed: 1949-07-08
Abstract: <PICT:0685620/III/1> <PICT:0685620/III/2> Dipropylamines are obtained in concentrated state from aqueous mixtures which are richer in amine than water-azeotrope, by submitting the given mixture to distillation in a fractionating column, taking-overhead vapours of the amine/water azeotrope, condensing the vapours, maintaining the condensate at a temperature between 40 DEG C and the boiling-point of the azeotrope whereby an amine-rich layer and a water-rich layer separate, and returning the amine-rich layer to the column.  The concentrated amine is obtained in the boiler of the column.  The process may be applied to both n- and iso-dipropylamine.  In an example, a mixture containing 72 per cent din-propylamine and 28 per cent water, was subjected to distillation using a column (1 inch diam.) packed with Raschig rings ( 1/8 inch), equivalent to 4 to 5 theoretical plates. An elbow-tube led from the top of the column to a vertical condenser which delivered condensate to one limb of a U-tube: this limb had a tube for the return of the amine-rich layer to the column, while the other limb had an outlet tube for leading the water to a measuring cylinder.  The U-tube was surrounded by a stirred water-bath maintained at 48 DEG C.  Further feed-mixture was introduced into the U-tube (via the condenser) during the distillation.  The din-propylamine which collected in the boiler contained only 0.2 per cent of water; while the water, which collected in the measuring cylinders, contained about 0.2 per cent of amine.  Another example relates to the dehydration of di-isopropylamine; in this case the decanter was maintained at 70 DEG C.  When the decanting is effected at a temperature close to the boiling-point of the azeotrope, the process may be carried out in the apparatus shown in Fig. 1.  The aqueous mixture is introduced at point 2 into column 1 which is heated by steam-coil 4.  The azeotropevapours pass through pipe 6 to condenser 5; and the condensate flows down through pipe 7 to decanter 8 which is situated within an upper extension of the column.  The amine-rich layer is returned to the column through outlet 10, while the water-layer is ejected through pipe 11.  Concentrated amine is withdrawn through pipe 12.  The aqueous mixture may be heated and subjected to a preliminary decantation before distillation, as shown in Fig. 2.  The mixture is introduced through pipe 2 into tank 13, where it is heated by the vapours from column 1, ascending through downcomer 16.  The heated mixture flows through aperture 14 into the downcomer where it joins the condensate from condenser 5.  The mixed liquids then flow through pipe 7 to decanter 8.  The water-layer obtained in any modification of the process, may be distilled for recovery of amine in a second column, from which the overhead-condensate is returned to the decanter associated with the first column, while water is rejected from the base of the second column.  If the aqueous amine-to-be-dehydrated contains less than 0.2 mole fraction of water, it is introduced into the column at a point situated several plates from the top of the column.  If the initial aqueous amine contains more than 0.1 mole fraction of propyl alcohol, it is subjected to preliminary extractive distillation with water; the overhead condensate from the extractive-distillation column which has substantially the composition of the amine/azeotrope, is decanted, and the amine layer is subjected to the process of the invention.